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.. include:: ../../../../common.defs

Setting a Transaction Hook
**************************

If the request does not have the ``Proxy-Authorization`` field set to
Basic authorization or a valid username/password, then the plugin sends
the 407 Proxy authorization ``required`` status code back to the client.
The client will then prompt the user for a username and password, and
then resend the request.

In the ``handle_dns`` routine, the following lines handle the
authorization error case:

.. code-block:: c

    done:
         TSHttpTxnHookAdd (txnp, TS_HTTP_SEND_RESPONSE_HDR_HOOK, contp);
         TSHttpTxnReenable (txnp, TS_EVENT_HTTP_ERROR);

If ``handle_dns`` does not find the ``Proxy-Authorization`` field set to
Basic authorization or a valid username/password, then it adds a
``SEND_RESPONSE_HDR_HOOK`` to the transaction being processed. This
means that Traffic Server will call the plugin back when sending the
client response. ``handle_dns`` reenables the transaction with
``TS_EVENT_HTTP_ERROR``, which means that the plugin wants Traffic
Server to terminate the transaction.

When Traffic Server terminates the transaction, it sends the client an
error message. Because of the ``SEND_RESPONSE_HDR_HOOK``, Traffic Server
calls the plugin back. The ``auth-plugin`` routine calls
``handle_response`` to send the client a ``407`` status code. When the
client resends the request with the ``Proxy-Authorization`` field, a new
transaction begins.

``handle_dns`` calls ``base64_decode`` to decode the username and
password; ``handle_dns`` also calls ``authorized`` to validate the
username and password. In this plugin, sample NT code is provided for
password validation. UNIX programmers can supply their own validation
mechanism.